This invention relates to a method for preparing free-flowing, water-soluble polymer gels and to the unique products thus obtained. More particularly, this invention relates to a method wherein a small quantity of an amphipathic compound is added to a water-soluble cationic, anionic, non-ionic or amphoteric polymer gel, thereby reducing the adhesiveness of the gel to itself and to other substances. This reduced adhesiveness allows the polymers of the instant invention to be stored in free-flowing form for long periods of time.
Water-soluble polymers can be prepared in several forms. For instance, it is known in the art that water-soluble polymers can be prepared in the dispersed phase of water-in-oil emulsions. These polymers are then generally sold as water-in-oil emulsions which contain 25 to 30 percent by weight polymer solids and an inverting surfactant.
Water-soluble polymers can also be prepared as aqueous solutions. However, since aqueous solution polymerization processes typically produce polymer gels which are viscous and difficult to handle as fluids, these polymers are usually sold as dry powders which contain 85 to 98 percent by weight polymer solids or as dilute aqueous solutions containing less than 20 percent polymer solids.
Disadvantages are inherent in all of the polymer forms mentioned above. For example, inverted water-in-oil emulsions generally are lower in activity than powdered polymers, emulsification may deleteriously affect the performance characteristics of the polymer, and oil and surfactant requirements keep manufacturing costs high. Powdered polymers are costly to produce due to the drying and milling steps required, and these operational steps may also degrade polymer quality. Dilute aqueous solutions of water-soluble polymers, though easy to handle, are costly to transport due to their low active polymer content.
Accordingly, the need exists for a low-cost method of preparing anionic, cationic, non-ionic and amphoteric water-soluble polymer gels which can be easily and economically handled, and which have improved performance characteristics and high polymer concentrations. Such an invention would satisfy a long-felt need and constitute a notable advance in the art.
U.S. Pat. Nos. 4,113,688 and 4,358,550 describe processes for rapidly dissolving water-soluble polymer gels into water to form dilute aqueous solutions in a manner which minimizes degradation of the polymers' physical properties, comprising extruding, cutting and slurrying the polymers in water, followed by subjecting the slurry to high shear forces and the addition of more water. The processes of these references do not, however, produce high solids polymer gels which are easily handled and which can be stored for extended periods of time in free-flowing form. Moreover, these processes require either the use of expensive make-down equipment at the use site or transportation of dilute polymer solutions.
U.S. Pat. No. 4,134,871 discloses a method for reducing the adhesiveness of acrylamide-type polymers comprising adding polyethylene glycol to these polymers during manufacture, thereby allowing mincing and drying with minimum adhesion. Like references U.S. Pat. Nos. 4,113,688 and 4,358,550, reference U.S. Pat. No. 4,134,871 does not disclose a method for production of high solids polymer gels which can be easily handled and stored for long periods of time without agglomeration.
One aspect of this invention relates to a method for preparing free-flowing, water-soluble polymer gels. This method, aside from minimizing agglomeration of polymer gel particles, obviates the drying and milling steps required in other manufacturing processes, thereby lowering production costs while minimizing product degradation due to processing. The unique products made by the inventors' process are free-flowing, high molecular weight, cationic, anionic, non-ionic and amphoteric water-soluble polymer gels. These gels remain free-flowing and readily soluble after storage for extended periods of time. Also, these gels remain free-flowing after multiple freeze-thaw cycles and after storage at elevated temperatures.
Another aspect of the invention relates to a free-flowing polymer gel admixture comprising size-reduced polymer gel particles and an amphipathic compound.